The present invention is directed to processes for laminating rigid substrates, systems for laminating rigid substrates, adhesives for laminating rigid substrates, and products laminated using the processes, systems, and adhesives of the invention. In particular, the present invention includes processes and systems for laminating two or more rigid substrates to one another.
Cathode ray tubes (also known as CRTs) are specialized vacuum tubes which produce images by striking a phosphorescent surface with electron beams. CRTs are commonly used in television sets, computer monitors, and other displays. Typical CRTs include at least one electron gun, a glass tube, and a glass screen or display. The interior surface of the screen contains phosphors, and the electron gun generates beams of electrons that strike the phosphors and produce visible spots of light.
CRTs have been in use for decades, and the screens (that portion exposed to viewers) of traditional CRTs have a slightly convex exterior surface. This convex exterior surface has been necessary in part to maintain the strength of the screen, but results in undesirable distortion of the image. In recent years technological advances in CRT design and manufacturing have permitted the creation of CRTs that have flat or nearly flat screens. These flat CRTs create less image distortion than previous curved CRTs, and result in an improved display.
The tube and screen of CRTs are manufactured from glass. The various properties of glass, including temperature stability, light transmission, scratch resistance, durability, and electrical resistance make it an excellent CRT material. Unfortunately, the glass used in most CRTs is relatively reflective. This reflectiveness can result in distracting and annoying reflections in the CRT display. Therefore it is desirable to improve on CRT displays by providing a surface on the CRT display that reduces reflection.
One approach to providing a low reflective CRT screen is to position a transparent after-market anti-reflective surface in front of the screen. These anti-reflective surfaces, such as antireflective filters sold by Minnesota Mining and Manufacturing Company (3M) of St. Paul, Minn. can be very useful at reducing reflection, and are particularly effective because they permit retrofitting and a improvement of millions of existing CRTs. Although these anti-reflective after-market products are well suited for many purposes, it would also be desirable to secure during manufacture an anti-reflective material directly to the front surface of the CRT or other flat glass display, such as plasma displays. This would permit the anti-reflective surface to be durable and inconspicuous.
An alternative approach for providing a low reflective screen is the use of anti-reflective materials such as anti-reflective glass and coatings on polymeric films. Anti-reflective optical films, including optical films for cathode ray tubes and flat panel displays have been produced. Unfortunately, these films have generally failed to provide the same level of anti-reflectiveness as glass, are more easily scratched, and are not as flat as most anti-reflective glass.
In contrast, anti-reflective glass is a good material for reducing reflection. Anti-reflective glass is durable, has good anti-reflective properties, and can be produced such that it is very flat. Unfortunately, anti-reflective glass is a rigid or substantially rigid material that is difficult to permanently adhere to the front of CRTs. One problem associated with adhering glass to the front of a CRT is that air bubbles are easily entrapped between the glass and the CRT when the glass is bonded to the CRT. This problem is significant because even a single bubble trapped between the two panels can diminish the effectiveness of the display if the bubble is readily visible. A need also exists for a method to adhere the glass to the CRT that is quick and cost effective, with a minimum of waste.
In addition to methods and systems for adhering anti-reflective glass to CRTs, a general need exists for methods and systems for adhering other rigid substrates to CRTs and other displays. For example, it is often desirable to install a polarizing material on the outside of CRTs, including rigid glass polarizing filters. These polarizers may include circular polarizers. Such rigid substrates are also desirably installed on other types of substrates besides CRTs, including liquid crystal displays, plasma display panels, and other flat displays. Other useful rigid substrates include antistatic materials, anti-radiation substrates, and conductive substrates (such as those with an iridium tin oxide (ITO) coating). Although it is desirable to adhere these rigid substrates to one another, it is often difficult to efficiently and economically conduct such processes with a minimum of waste and with a consistently high quality product that is free of defects.
Therefore a need exists for a method and system to adhere two rigid or substantially rigid substrates together, including a method and system for adhering a glass sheet to a CRT display or other type of display.
The present invention is directed to methods, systems, and materials for adhering rigid substrates to one another. The invention includes a process for lamination of anti-reflective glass to the screen of a CRT display, particularly to a flat-screen CRT display. The invention also includes processes and systems for laminating other rigid and substantially rigid materials to one another.
The method may include providing a first rigid substrate having a first surface, and a second rigid substrate having a second surface. The first rigid substrate is distorted to create a curvature in the first surface, and an adhesive composition is applied to at least a portion of the second surface of the second rigid substrate. The curvature of the first surface of the first substrate is brought in contact with the adhesive on the second surface in order to form an-interface having a contact front. Thereafter, the contact front of the adhesive advances across at least a portion of the second substrate in order to distribute the adhesive between the two rigid substrates and permit their bonding together. The order of performing these steps is typically not critical, and the steps may be performed in different orders.
In one implementation of the invention the first rigid substrate comprises a sheet of anti-reflective glass, and/or other optical coated glass such as glass with a transparent conducting coating or neutral density coating, and the second rigid substrate comprises a screen of a flat CRT or other display. The process and system allow for bonding of the anti-reflective glass to the CRT with reduced likelihood of entrapping air bubbles between the two substrates, thereby permitting consistent high quality displays having low reflectivity and few defects, if any, in the lamination between the substrates.
As used herein, the term xe2x80x9crigid substratexe2x80x9d refers to substrates that are rigid or substantially rigid. For example, rigid substrates include glass sheets and rigid polymeric sheets. The first rigid substrate should have enough flexibility to allow deformation sufficient to allow formation of a curve in the first surface. Typically, the first rigid substrate is a thin sheet of glass which has adequate flexibility for the methods and process of the invention. The glass is typically less than 3.3 millimeters in thickness, and more typically less than 1.6 millimeters in thickness. However, other thicknesses of this first rigid substrate are appropriate provided a shallow curve can be formed in the substrate. The second rigid substrate is not typically deformed during application of the first rigid substrate. Therefore, the second rigid substrate can be as rigid as, or more rigid than, the first rigid substrate.
As used herein, the term flat includes surfaces that are substantially flat. It will be appreciated that even flat surfaces as used herein will have measurable variations, and are therefore not perfectly planer. For example, a flat surface as used herein may have a standard deviation in surface elevation from about 0.1 to 0.6 mm, and typically from about 0.2 to 0.3 mm. Although the present invention is well suited to use on flat surfaces, it is also suitable for use on various surfaces that have curvature, typically a slight curvature, or slight surface irregularities.